Magnetoresistive Random Access Memory (MRAM) is an emerging technology that may be competitive with prior integrated circuit memory technologies, such as floating gate technology. The MRAM technology may integrate silicon-based electronic components with magnetic tunnel junction technology. A significant element in MRAM is the magnetic tunnel junction (MTJ) where information may be stored. The MTJ stack has at least two magnetic layers separated by a non-magnetic barrier, where a fixed layer (e.g., reference layer) has a set magnetic property and a free layer (e.g., storage layer) has a programmable magnetic property for storing information. If the fixed layer and the free layer have parallel magnetic poles, the resistance through the MTJ stack is measurably less than if the fixed layer and the free layer have anti-parallel poles, so parallel magnetic poles may be read as a “0” and anti-parallel poles may be read as a “1.” The MTJ stack is typically incorporated into a memory cell, and many memory cells with MTJ stacks are incorporated into a memory bank.
The magnetic properties of the free layer are changed when the memory cell is programmed, where the alignment of the free layer magnetic properties is switched or changed relative to the fixed layer magnetic properties in the programming process. Programming changes the magnetic properties of the free layer relative to the fixed layer from anti-parallel to parallel, or from parallel to anti-parallel. The programming process typically includes applying a charge (e.g., voltage) across the MTJ stack such that a programming current passes through the MTJ stack.
Thermal stability of the MTJ stack for retaining stored information in the free layer is dependent on an energy barrier of the free layer of the MTJ stack, where higher energy barriers provide greater thermal stability for data retention (e.g., energy barrier(data_retention)>40 kT, where k is Boltzmann's constant and T is temperature). The energy barrier of the free layer should be sufficiently high to maintain thermal stability, for example, from about room temperature (e.g., about 25° C.) to packaging reflow process temperatures (e.g., solder reflow process temperatures of about 260° C.). To achieve relatively high switching efficiency and data retention over a desired temperature range, the stray field from the fixed layer acting on the free layer should be relatively low over the temperature range. However, many conventional fixed layer materials have magnetic moments that are very temperature dependent, producing at various temperatures, for example, at or near packaging reflow process temperatures, a significant stray field from the fixed layer. As a result of this significant stray field, a relatively high magnetic field coupling strength (Hcpl) at the free layer may be produced that can overcome the energy barrier of the layer, thereby causing data retention issues.
Accordingly, it is desirable to provide integrated circuits with magnetic tunnel junctions having enhanced data retention over a relatively broad temperature range, as compared to traditional magnetic tunnel junctions, and methods for fabricating such integrated circuits. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.